The present invention relates generally to the field of transducers, and in particular to rotationally aligning transducers on opposite sides of a barrier, and to attaching transducers to submerged surfaces.
A transducer is a device that converts one form of energy to another. Transducers may be used, among other functions, to transmit and receive data or power across a solid barrier without requiring any holes in the barrier. Conceptually, this can be done by a first transducer on one side of a barrier turning electrical energy into mechanical energy, the mechanical energy traveling across the barrier, and being received by a second transducer on the other side of the wall which converts some portion of the mechanical energy back into electrical energy. This ability is particularly useful for transmitting energy and data through barriers like ship and submarine hulls, pressure vessel tanks and other walls separating extreme environments where it is often undesirable to create openings for wires.
FIG. 9 is partially taken from published patent application US2010/0027379, and shows a pair of axially aligned piezoelectric ultrasonic transducers 12 and 16 that are acoustically coupled to opposite surfaces 20 and 24 of a steel wall 22 that may be the hull of a ship or submarine or other barrier.
Ideally, ultrasonic communication transducer devices should be attached directly to the communications barrier. It is generally desirable to have a smooth, uninterrupted, uniform barrier between coupled transducers.
The attachment of transducers to solid barriers is often simple in dry laboratory or factory environments. Although it may be relatively simple to affix transducers to the surface of oceangoing vessels when such vessels are in dry dock, it will sometimes be preferable to install transducers below the water line without the expense, delay, and difficulty of moving a large ship out of the water.
Proper transducer attachment is extremely difficult in an underwater environment such as a submerged portion of a ship's external hull, however, for a variety of reasons. First, it is usually desirable to remove all water, as well as any other extraneous substances, from the attachment surface. It is also difficult to apply and retain epoxy or other adhesives in an underwater environment, and to provide the conditions necessary for such adhesives to harden or cure properly. It is often necessary to provide a sustained loading force at the attachment site while an epoxy or adhesive sets, which poses additional challenges when the surface is submerged. Thus, there is a need for apparatus and methods for removing and excluding water from a submerged transducer attachment surface, for applying adhesives to submerged attachment surfaces, and for applying sustained pressure to such surfaces to allow adhesives to set. It is particularly desirable to have apparatus and methods for both direct attachment of transducers to underwater substrates, and for attachment utilizing an intermediary layer.
Furthermore, it can be difficult to align transducers on opposite sides of a surface, such as the hull of a large ship or a submarine, when only one side of the surface can be seen at a time. Techniques have been developed to positionally align transducers across a ship's hull using signal peaking at a single point. See WO2011/027168 and WO2011/027169, both to Bagshaw et al. Single point peaking techniques are not well suited, however, for aligning a plurality of transducers in a single compact arrangement through a hull because such arrangements must be aligned axially as well as positionally, and rotational alignment cannot be determined using a single peaking point. Thus, it is desirable to have a convenient method for determining rotational alignment across a hull using a plurality of peaking points corresponding to a plurality of spaced transducers.
Transducers may be mounted to communications surfaces such as hulls either directly, typically one at a time, or using an intermediary layer which may carry multiple previously-configured transducers.
Direct attachment is the preferred coupling method. Direct attachment minimizes the number of interfaces between transducers on opposite sides of the barrier, which results in greater transfer efficiency and less interference. Hull curvature can cause variations in the thickness of the adhesive layer between flat transducers and plates, and rounded communication surfaces they are attached to. Any curvature of the communication surface is less significant using direct attachment because each transducer will have a smaller area than a larger intermediary plate.
It can be difficult to align multiple directly attached traducers across a barrier because direct attachment is often done one transducer at a time. Thus, methods for aligning multiple transducers being mounted directly to a submerged hull are needed. Direct attachment can also be difficult because individual transducers, such as piezoelectric crystals, are often fragile. As a result, handling individual transducers, and holding them against the communication surface during adhesion, risks breaking the transducers.
Attachment using an intermediary layer, such as transducers on top of a metal plate, is easier because multiple transducers can be attached to the single plate in precise alignments in a factory setting. It can be easier to align two intermediary plates across a hull, each plate carrying several transducers, than to align a large number of individual transducers, two at a time in the field. An intermediary plate can also carry all the electronics that are needed to be attached to the transducers it carries. This avoids the difficulty of trying to attach electronics to transducers, underwater, after they have been mounted to a ship. It can also be easier to handle fragile transducers that are pre-mounted on a durable metal plate because any pressure required during the adhesion process can be placed on the intermediary plate instead of on the fragile transducers themselves.
The main disadvantage of using an intermediary plate is that signals traveling between transducers must cross a greater number of interfaces, increasing signal reflections and interference. Thus, transducers mounted on intermediary layers may be less efficient. It is also difficult to achieve minimal and uniform adhesive thickness between a flat intermediary plate and a curved communication surface because an intermediary plate will have a greater surface area than individual transducers. This excess adhesive may also reduce transducer efficiency.